Compact fluorescent lamps (CFLs) are a variety of fluorescent lamp, typically comprising fluorescent tubes which are bent or curved into a compact shape, to provide high luminous output with minimal form factor. They are designed in particular to provide high energy efficiency replacements to traditional incandescent light bulbs. An example of a standard prior art CFL lamp 10 is depicted in FIG. 1, for example.
Increasingly, however, solid state lighting is becoming a preferred option in both domestic and commercial applications, due to its extremely small form factor, long lifetime, high lumen efficiency, low operating voltage and fast modulation of lumen output. For this reason a number of LED replacement CFLs have been developed, comprising LED elements arranged to provide a luminous output having the same light distribution as CFLs and traditional incandescent bulbs.
However, provision of light over such a broad angular distribution (essentially) 360° requires a large number of LEDs, positioned in close proximity, to generate a large overall output flux. With such a high concentration of LED elements, efficient heat dissipation becomes problematic, leading to higher than optimal operating temperatures and a consequent deterioration in LED lifetimes. Moreover, the large number of LED components increases unit costs and seriously affects the energy efficiency of the lamps.
In response to these problems, a number of devices have been developed aimed at improving the light output efficiency and reducing the total number of required LED elements. FIGS. 2 and 3 show two examples of such proposed devices 12, as disclosed in US 2014/328065. Each comprises LED elements (not shown, but having position indicated by 18), arranged facing a light exit window 16, the window constraining the luminous output direction of the device 12 to just a limited range of output angles. In particular, both are adapted to produce a luminous output directed along, or arced around, just a single predominant axial direction (i.e. a luminous output having an angular width less than or equal to 180°). This means that energy is not wasted propagating light in directions in which it is not needed; luminous output may be concentrated across an area where it is most useful.
However, such directional devices carry clear disadvantages in terms of the scope of their applicability. Each is designed to connect into an existing light fitting, having most typically a fixed orientation. Hence, each of the bulbs of FIGS. 2 and 3, for example, can only ever be useful within a limited subset of lighting arrangements: those wherein the orientation of the fitting is such that the output window of the device, once the device is installed, is oriented facing in the intended output direction of the light fitting.
FIGS. 4-7 illustrate this difficulty. In FIGS. 4 and 5, the lamps of FIGS. 2 and 3 are respectively shown installed within a first example luminaire 22 having a first shape and orientation. As can be seen, only the lamp of FIG. 2 distributes light effectively from the luminaire, with the lamp of FIG. 3 directing much of its luminous output toward the walls of the luminaire, and not toward the lower output area. Similarly, FIGS. 6 and 7 show the lamps of FIGS. 3 and 2 installed respectively within a second example luminaire 24, having a second shape and orientation. In this case, it can be seen (FIG. 6) that only the lamp of FIG. 3 emits light in an effective manner from the luminaire, while in FIG. 7, almost all of the light of the lamp of FIG. 2 is directed toward a wall of the luminaire.
For directional lamps, therefore, the particular shape, style and light-output orientation of the lamp must be carefully chosen for each intended application. This confers numerous disadvantages for both distributers and retailers, but also users. In the case of retailers, a large number of different lamp varieties must be stocked at any one time, so that a buyer can be sure to find a lamp which is appropriate for their particular existing luminaire arrangement. This naturally increases stock costs, and overhead costs in terms of storage and display space. For end users too—particularly domestic users—the necessity of having to work out which of a large stock of lamps is in particular appropriate for their light fitting is extremely burdensome, and indeed risks frustration and significant inconvenience in the case that they choose an inappropriately shaped or oriented lamp in error. For example, it is very difficult to tell in advance, in which particular direction the light output window of the device of FIG. 2 will be facing once screwed or twisted into the electrical fitting of a luminaire.
Desired therefore is a LED lighting device, suitable for replacing existing compact fluorescent lamps, which offers improved luminous and thermal efficiency compared with pan-directional replacement devices, but which does not incur the above described disadvantages of limited range of applicability and the consequent costs therefore both in terms of money (to a retailer) and convenience (to an end user).
U.S. Pat. No. 7,473,007B1 discloses an adjustable lamp which includes a lamp and a scattering shade which is slidable on the lamp. The scattering shade has a front end coupled with a reflective blade which is bent at a selected angle to reflect light. By sliding the scattering shade on a light penetrative shade, the position of the reflective blade can be changed to alter the reflective direction of the light.
FR2864203A1 discloses a solar lighting device, which has LEDs producing directional lighting, and annular side wall producing diffused lighting, where reflecting surfaces are moved relative to LEDs between positions for obtaining diffused and directional lighting.
US2012/0026732A1 discloses a lamp which includes a bulb comprising at least a partially light-transmissive material, a lamp base for fitting the lamp in a socket and feeding electrical energy, an illuminant arranged in the bulb. The illuminant comprises a first light source and a reflector configured for directed emission of light output by the first light source, and the reflector is arranged rotatably about the light source, wherein the control lever is coupled to the reflector and the control lever can be displaced by a user to vary the emission direction of the light produced during operation of the lamp.